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Investigations of magnetic field diffusion and plasma resistivity in 12-cm-diameter triple-gas-puff Ar Z-pinch implosions were carried out by using planar laser-induced fluorescence (PLIF), a laser shearing interferometer (LSI), and a laser wavefront analyzer (LWA) on a 3.5-MA 200-ns generator. The PLIF measurements gave the initial Ar gas distributions. The implosion velocity and electron density profiles were measured from LWA and/or LSI. From these, the implosion plasma sheath thickness, ion density, mean ion charge states, temperatures, and implosion velocity are obtained, which allows us to calculate the classical plasma resistivity. A 1-D analytic magnetic field diffusion model is constructed and used to predict the imploding plasma sheath thickness and its resistivity. Based on comparisons of the experimental measurements and the diffusion model prediction, we found out that plasma resistivity is enhanced by the cross-field diffusion above the classical value, as high as 60 times the Spitzer's value. Details are given in this paper.

We report an approximate energy distribution (coarse spectrum) over the range ~0.1 to > 10 keV for the X-ray output of an argon Z-pinch. The tests, conducted at ~15-MA peak current, utilized an 8-cm diameter double-shell nozzle. Sze (2001) have previously described the performance of this Z-pinch with emphasis on the K-shell line emission at ~3 keV. Additional measurements that address the non-K-line output of the Z-pinches are presented here. On the one hand, > 4-keV photons due to the free-bound continuum constitute a significant fraction, almost 30%, of the nominal K-shell emission. On the other hand, the sub-3-keV L-shell lines and continuum show distinctive time histories and significant yields. These nonresonance-line emissions are important for a more complete understanding of the implosion physics, for proper analysis of diagnostic responses, and for their effects upon objects exposed to the Z-pinch's radiation

Time-resolved measurements of the absolute free-bound (FB) continuum spectrum emitted from a 12-cm-diameter argon gas-puff Z-pinch driven at ~6-MA peak current with 220- to 260-ns implosion times are reported. A crystal spectrometer is used with silicon diode detectors to provide kiloelectronvolt spectral resolution. The energy and absolute-intensity calibration procedures for the spectrometer are described. The slope of the FB continuum is well represented by a decaying exponential spectrum with a single electron temperature from which spatially averaged, time-resolved (Te(t)), and time-integrated (langTerang) electron temperatures are inferred. An expression for the absolute FB continuum, which takes into account recombination onto bare as well as H-like species, is presented and used to infer time-integrated spatially averaged ion densities langnirang. The values of langTerang and langnirang are in general agreement with the values of these quantities obtained by using the conventional K-shell line-ratio method. Values of Te(t) peak on the rise of the continuum radiation pulse and gradually decrease during the pulse. The fraction of the total energy radiated in the K-shell that resides in the FB continuum is 6%-10%, and this fraction increases with langnirang. Calculated continuum spectra are in agreement with measured spectra

We have developed a 12-cm-diameter Ar gas Z-pinch load, which produces two annular gas shells and a center gas jet. The two-dimensional (2-D) gas density profiles of the load, in r-/spl theta/ and r-z planes, were measured with submillimeter spatial resolutions using the planar-laser-induced fluorescence (PLIF) method, for conditions used in Z-pinch experiments. Due to interactions between the shells, the net gas density profile differs from the superposition of the individual shell profiles. Narrow density peaks are observed both at smaller and larger radii than the radius where the shells come in contact with each other. Two-dimensional flow velocity distributions are determined from the displacements between the fluorescence and later time phosphorescence images. The measured stream velocities of argon gas puffs are 650 /spl plusmn/ 20 m/s, higher than the ideal gas velocity due to the formation of clusters in the supersonic gas flow. Indeed, clusters were observed in earlier Rayleigh scattering experiments. The gas measurements of the initial phase using the PLIF will be combined with other density measurements of the implosion and pinch phases to better understand the implosion dynamics and to provide initial conditions for simulation codes.

Recently, an 8 cm diameter double-shell nozzle has produced argon Z pinches with high K-shell yields with implosion time of 210 ns. To produce even longer implosion time Z pinches for facilities such as Decade Quad [D. Price, et al., “Electrical and Mechanical Design of the Decade Quad in PRS Mode,” in Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] (9 MA short circuit current at 300 ns), a larger nozzle (12 cm outer diameter) was designed and fabricated. During initial testing on Double-EAGLE [P. Sincerny et al., Proceedings of the 5th IEEE Pulsed Power Conference, Arlington, VA, edited by M. F. Rose and P. J. Turchi (IEEE, New York, 1985), p. 151], 9 kJ of argon K-shell radiation in a 6 ns full width at half maximum pulse was produced with a 240 ns implosion. The initial gas distributions produced by various nozzle configurations have been measured and their impact on the final radiative characteristics of the pinch...

Theoretical studies have predicted that the disruptive role of the Rayleigh-Taylor (R-T) instability on the current conduction and implosion characteristics of annular Z-pinch loads will be mitigated by mass accretion if uniform fill or multiple annular shell loads are used. Holographic interferometry was used to study these physical processes during the implosion phase of puff-on-puff loads on a terawatt accelerator. Both axial (r-z) density perturbation and azimuthal (r-/spl theta/) filamentation modes of the R-T instability were observed. Significant ionization (Z/spl ap/3-10) of the inner gas puff atoms was observed below the anode grid before the outer puff had imploded to this radial position. Radiation hydrodynamic calculations indicate that photoionization by radiation from the outer current carrying shell could not account for this ionization. Current flowing on the inner gas puff could be the source of this ionization. The effect of these physical processes on the radiation yield from z-pinches warrants further investigation.

We have applied the technique of acetone laser-induced fluorescence (LIF) to the measurement of gas distributions from axisymmetric supersonic nozzles used to produce loads for z-pinch plasma radiation sources. Typical peak particle densities are ∼1017 particles/cm3 for loads imploded on the Double-EAGLE facility. The experimental approach uses a pulsed laser (266 nm wavelength, 2.2 mJ per pulse, 5 ns pulse width, and 3×107 W/cm2 intensity) to obtain a snapshot along a chord through the center of the gas density distribution at an arbitrary axial distance, z, from the nozzle exit. We report measurements at 4.3 and 20.0 mm from the exit of the nozzle for comparison with previous measurements. We find acceptable agreement between LIF and laser interferometer measurements. Strengths of the LIF approach include simplicity of implementation and high radial spatial resolution.

The Doppler broadening of ion line profiles emitted by z-pinch plasma provides information about the thermalization of the implosion kinetic energy and the radiation efficiency of the pinch. Measurements of these line profiles are often complicated by source broadening in the instrument and opacity broadening of the emitted radiation. A high resolution concave crystal spectrometer in the Johann geometry was used to record the time averaged spectra of optically thin trace elements in the load. An imaging slit provided radially resolved but axially averaged spectra. The measurements indicate that lower ion temperatures (3–5 keV) are observed for Al wire loads on both the Saturn and Double EAGLE accelerators in the short current pulse mode (60–100 ns) than in the long pulse mode (125–225 ns) where values of 6.3–9.5 keV are observed. These values are smaller than those observed on Saturn by others. Furthermore, the wavelength at the line center of axially resolved ion line profiles on the DM-2 accelerator at ...

A series of nickel z pinch experiments was conducted at 18 MA current on the Z accelerator producing up to 13 kJ of K-shell radiation at 7.8 keV and above. Double-shell wire arrays were used, with the diameter of the outer array of the nested structure varied from 55 to 70 mm. By using Cr and Mn dopants in conjunction with a streak spectrograph, the interaction of the outer and inner array could be investigated. The radiation from the outer array E array started slightly after the inner array and lasted longer, producing comparable energy per atom at lower power. This indicates that the arrays were well mixed for most of the radiation pulse, in contrast to the observed behavior of a double-shell gas puff.

High-sensitivity interferometry measurements of initial density distributions are reviewed for a wide range of gas-puff nozzles used in plasma radiation source (PRS) z-pinch experiments. Accurate gas distributions are required for determining experimental load parameters, modeling implosion dynamics, understanding the radiation properties of the stagnated pinch, and for predicting PRS performance in future experiments. For a number of these nozzles, a simple ballistic-gas-flow model (BFM) has been used to provide good physics-based analytic fits to the measured r, z density distributions. These BFM fits provide a convenient means to smoothly interpolate radial density distributions between discrete axial measurement locations for finer-zoned two-dimensional MHD calculations, and can be used to determine how changes in nozzle parameters and load geometry might alter implosion dynamics and radiation performance. These measurement and analysis techniques are demonstrated for a nested-shell nozzle used in Double Eagle and Saturn experiments. For this nozzle, the analysis suggests load modifications that may increase the K-shell yield.

During the last few years, we have concentrated on developing plasma radiation sources (PRS) for the longer current rise time (up to 300 ns) of the direct-drive Decade Quad (DQ; Price et al., 1999). In particular, we have developed an argon gas-puff PRS that produces a high quality pinch with an ∼200-ns implosion time, twice the implosion time of typical z pinches. We have shown that large-diameter, solid-fill (i.e., the gas density is a smooth function of the radial distance rather than a discrete shell) gas puffs can achieve adequate heating and stability for long-implosion z pinches with good K-shell yield.

The first observations of gaseous load implosions with over 15 MA in >110 ns on the Z generator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] are reported. Starting from a diameter of over 8 cm, an argon double-shell Z pinch imploded to under 0.5 cm K-shell emission diameter. With a load mass of 0.8 mg/cm, K-shell x-ray output reached 274±24 kJ in a 15 TW peak power, 12 ns pulse. This record-high yield is consistent with the current-squared scaling predicted for the “efficient” emission regime.

Hardware and software have been developed for recording and displaying accurate image and spectral data produced by z-pinch plasma radiation sources at the Double-EAGLE facility at Maxwell Physics International. Desktop computers are used to acquire the data, analyze it, and display and print the results. Of the four charge-coupled device (CCD) image recording systems implemented, two record x rays directly and two record optical light emission from electron–excited phosphors. The CCD systems required careful shielding to allow them to operate in the harsh radio frequency noise environment. During a series of shots at the SATURN facility at Sandia National Laboratories, the quality of a keV x-ray spectrum recorded directly with a CCD compared well with an equivalent spectrum recorded with 2497 film.

Solid-fill nozzles for long-implosion Z-pinch experiments to produce argon K-shell x rays (photon energy >3.1 keV) have been developed. With a 7 cm diam nozzle, which is appropriate for a 200 ns driver, stable implosions at 180 ns and 4 MA have produced peak argon K-shell yields exceeding 15 kJ. As previously seen with short (∼100 ns) implosion times, the K-shell yield scales as the fourth power of peak current, I4. Limited testing with a 10 cm nozzle, which is appropriate for a >250 ns driver, has also achieved a stable implosion.

Timely estimates of z-pinch plasma conditions can aid in the optimization of plasma radiation source K-shell emission. For example, a shell-on-shell argon gas puff has many parameters, such as the axial gas density profile, inner to outer shell mass ratio, total mass, and pinch load length, which can be varied on a shot by shot basis. At the Double-EAGLE facility at Maxwell Physics International, digital cameras have been implemented to routinely record pinhole images, x-ray spectra, and axially resolved streak images. A computer algorithm has been implemented to take as input the data (pinch diameter, Ar Lyα to Heα line ratio, and K-shell power) and output the plasma parameters (density, electron temperature, and K-shell-emitting mass) as a function of z-pinch axial location. We describe the algorithm and present results for three different z-pinch loads.

We have developed a dual-plenum gas valve coupled to a double shell nozzle for the generation of “shell-on-shell” gas loads in z-pinch plasma radiation source experiments. The gas density profiles of the nozzles have been characterized with laser interferometry. This valve/nozzle combination has been successfully fielded on the Double-EAGLE and Saturn pulsed-power generators. The design and characterization of the shell-on-shell valve/nozzle are presented in this article.

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High-current (1–3 MA) reflex triodes are being developed as intense pulsed sources of moderate energy (200–1200 kV endpoint) bremsstrahlung. The triode consists of three coaxial electrodes: two hollow cylindrical cathodes and a flat anode foil between them. The grounded cathodes emit electrons that produce bremsstrahlung in the positive high voltage anode. The anode is made from thin tantalum (small fraction of the electron range) to minimize attenuation of the low energy portion of the x-ray spectrum. The electrons must make many passes through the tantalum to efficiently lose their energy and produce x-rays. This process is called reflexing. The triode configuration is thought to be the best way to accomplish this.

FEYNMAN is a LaTeX macropackage which allows the user to construct a versatile range of Feynman diagrams within the text of a document. Diagrams of publication quality may be drawn with relative ease and rapidity.

We carry out an energy-inventory analysis for a 12-cm-diameter, argon gas-puff shot on the Saturn generator. From the measured pinch inductance time history, we infer the average radius of the pinch current, r ind , and the total work done on the pinch, E coupled , both as functions of time. The kinetic energy as a function of time, E KE , is inferred from r ind and the measured initial mass distribution, assuming all of the mass is accreted as in a snowplow. The results show that early in the implosion, E coupled ≈ E KE . However, when the pinch begins to radiate significantly, E KE begins to decrease while E coupled continues to increase. The increase in coupled energy goes into plasma internal energy, E int , i.e., ionization and thermal energies of the z-pinch plasma, and total radiation, E rad . During the time of K-shell emission, the significant (∼ 150-kJ) increase in E coupled is reflected in approximately the same increase in E rad . There is agreement between E int at the time of peak K-shell emission inferred from E coupled and measurements of E rad , and E int inferred from independent spectroscopic measurements combined with an atomic-physics model.

Summary form only given. We wish to maximize the K-shell yield from high-atomic-number Z pinches (photon energy of ~1-8 keV) and to develop Z-pinch-based concepts for sources of higher-photon energy (~8 to 40 keV). To achieve these goals, large-diameter implosions are needed to: (a) produce the high specific energy required to excite K-shell line radiation from high-atomic-number Z pinches, (b) properly match the load to high-current (ges 10 MA) generators, and (c) develop continuum-radiator concepts that require ionizing beyond the optimum He/H-like state for K-shell emission. Large-initial-diameter implosions are also required for efficient coupling between the Z pinch and a generator with a long current rise-time (> 100 ns) and, thus, desirable lower voltage. The expected deleterious effects on final pinch formation associated with the increase in instability growth at larger diameter (e.g., Rayleigh-Taylor) can be mitigated by using an initial mass profile that is strongly peaked on axis. We review recent experiments with, and numerical simulations of, 12-cm initial diameter, argon gas-puff Z-pinch implosions. The experiments were carried out on the Decade Quad at implosion times of 230 to 250 ns and on Saturn at 200 to 215 ns. Both generators provide peak currents of about 6 MA. The argon K-shell yield was 80 kJ on DQ. On Saturn, we obtained 75 kJ of K-shell yield, roughly twice the maximum argon K-shell yield previously obtained there with a several-cm diam. nozzle at < 100 ns implosion times. Numerical simulations are in agreement with the measurements.

Summary form only given. Characterization of implosion kinematics is of interest in understanding and optimizing plasma radiation source (PRS) K-shell yield. It also serves to provide input parameters to the modeling of PRS pinch conditions. A measure of the sensitivity of the PRS implosion kinematics to changes in initial conditions is the time and axial dependence of the Z-pinch assembly on-axis and its associated K-shell yield. A relatively simple and routine PRS diagnostic is the so-called zipper array, which can characterize both the time and axial dependence of the pinch assembly (zippering) and the pinch x-ray yield. The zipper array is essentially a one-dimensional (1D), time-resolved imager, typically consisting of a linear array of X-ray power sensors (photo-conductive detectors: silicon diodes or diamonds), viewing the pinch through a transverse slit, with appropriate pre-detector filtering selecting the X-ray detection range of interest. We report here a study on the time dependent axial characterization of the pinch assembly and the K-shell yield for argon PRS shots taken with two different current drives, differing both in magnitude and waveform shape, and with implosion times in excess of 200 ns. The first current driver reached a peak current plateau of about 3.5 MA in 100 ns, which persisted at nearly constant current for an additional ~100 ns. The second driver delivered a nominally linear current ramp exceeding 6 MA in 300 ns. The study characterizes the final pinch assembly under both fixed and varied initial conditions. For nearly identical initial conditions, the data generally show a significant degree of reproducibility in the relative zipper timing, but with some variation in the K-shell yield at a given axial position. Changes in initial conditions can have a significant effect. For example, shots without pre-ionization changed the axial time dependence of final pinch assembly and axial distribution of K-shell yield.

Summary form only given. Structured 12 cm diameter Ar gas puff loads have produced Rayleigh-Taylor stable implosions and K-yields close to 1D hydrocode predictions. In order to optimize the designs of future loads, it is important to identify the reasons for these stable implosions. Diagnostics of the K-shell (3 keV 15 nsec and rises to a peak relatively slowly (~15 nsec). At locations where the XUV emission rises abruptly (les5 nsec), close in time to when the K-emission initiates, the K-emission is weaker. This observation is consistent with calculations that predict improved K-emission when shock preheating of the load mass is followed by quasiadiabatic compression

Summary form only given. The ability to control and vary the radial profile of the initial mass distribution for Z-pinch implosion is critical to both increase the K-shell X-ray yield and to elucidate the physics that determine pinch quality and yield. Toward that end, we have developed a triple-plenum gas valve that feeds a nozzle consisting of 2 concentric shells and an axial jet. Each plenum is independent in terms of gas pressure and constituents, affording the required flexibility. We will report on the results of experiments performed with this nozzle on several different pulse power generators covering a range of peak currents and implosion times

Summary form only given. Absolute measurement of the free-bound (FB) continuum spectrum above the K-shell from atomic-number Z ges 10 Z-pinches can be a useful diagnostic tool to obtain the electron temperature and the ion density of a hot, radiating Z-pinch. These measurements are also of interest for benchmarking continuum radiation models associated with the use of this high-photon-energy radiation for radiation-matter interaction studies. In previous work, we described a curved crystal spectrometer modified to measure, absolutely, the argon FB spectrum from 5 to 10 keV emanating from the implosion of a 12-cm diam, shell-on-shell, argon-gas-puff Z pinch, driven by peak currents of ~6 MA with implosion times of 220-260 ns on the decade quad. Time averaged and time resolved electron temperatures were determined from the slope of the FB spectrum and the energy in the FB spectrum was compared with the total K-shell yield. Now, we review the diagnostic and discuss an improved absolute calibration. The new calibration results in ~10% of the total K-shell yield residing in the continuum above 4.4 keV, about a factor-of-three lower than previously reported. We present new calculations that relate the ion density, electron temperature and absolute continuum emission that account for radiative recombination on both bare and H-like ions. Using radial and axial scale lengths obtained from time-integrated pinhole-camera images, this expression is used to infer the time-averaged density of ions radiating in the FB continuum, which is then compared with ion densities determined using the line-ratio technique. Finally, these measurements are compared with results from a CRE-based model that includes radiation transport

There is strong interest in many laboratories worldwide in utilizing less expensive, longer rise‐time (> 200 ns) pulsed power to drive x‐ray producing z‐pinches. Based on the idea of a magnetically‐driven annular implosion, the emission of K‐shell photons requires high energy per ion (implosion velocity above 43 cm/μs for argon) to strip the atoms to the helium‐like and hydrogen‐like states. This high velocity must be combined with high density in the final hot plasma to produce significant x‐ray yield. To first order, implosion velocity correlates with the initial diameter of the z‐pinch load in proportion to the implosion time. Thus some effort has been made in the last few years to develop larger diameter z‐pinch loads suitable for use with the longer rise‐time drivers. Advancing from the

A fast Marx (220 kJ, 450 nH, 675 kV) has been developed as a driver for an electron beam generator. This generator uses an inductive store with an opening switch to compress and amplify the power pulse. The 220 kJ Marx consists of four parallel 55 kJ Marxes to minimize the inductance. The 220 kJ Marx has been used to develop vacuum opening switches. These opening switches have demonstrated up to 22% efficiency and pulse compression of 5 to 1. Two switch concepts have been successfully tested as electron beam diodes on this Marx bank. The energy delivered to diode, the output voltage and power produced by this new high power generator will be presented. This generator serves as the proof-of-principle demonstration of inductive store/opening switch technology as an alternative to conventional capacitive store waterline technology.

The authors are developing an L-band (1.3 GHz) high current relativistic klystron amplifier for both long pulse ({ge} 500 ns) and high repetition rate ({ge} 200 pps) capabilities. In repetitive operation, it has produced 3.3 kW of average power in 80 ns FWHM pulses of 250 MW peak power at 200 pps. They are currently transferring this same klystron to a single-shot, long-pulse driver to demonstrate its operation with a {ge} 500 ns electrical pulse.

Summary form only given. While the characteristic "resonance" lines dominate the K-shell X-ray emission from Z pinches, the energy in the K continuum (free-bound and free-free transitions) can be significant. A simple model implies that the continuum could supply well over 10% of the K-shell yield if the plasma is warm enough and dense enough. We present here new measurements of the continuum strength for argon implosions. The data were taken at peak currents of 3.5 MA with implosion times exceeding 200 ns. Heavily filtered GaAs photoconductive detectors (PCD) were used as direct measures of the argon continuum above ~4 keV. Other major diagnostics included X-ray power sensors, calorimeters, time-integrated CCD spectra and CCD pinhole images. By combining the data from all of these instruments, we have derived the strength and temperature of the continuum as well as the yield in the K-lines using a self-consistent method. As implosion conditions changed, the changes seen in electron temperature (derived from K-line ratios) were not as large as the changes seen in the continuum temperature (derived from the PCDs). The yield in the continuum was close to a linear function of the K yield. The relative strength of the continuum does appear to depend on the detailed mass distributions produced by the 12 cm diameter nozzles used for these tests

We developed four types of GaAs PCDs: bremsstrahlung (two types), soft X-ray, and gamma for pulsed reactors. GaAs PCDs are advantageous in applications that require fast response, high dose rate, and/or neutron insensitivity. Desired detector sensitivity and response were obtained through modification of carrier lifetime by neutron irradiation, size of the sensing element, and orientation of the sensing element. The GaAs PCDs were used to characterize pulsed radiation sources in over 10 different tests and the measured data from these tests are presented. GaAs PCDs (E7 - E11 rad(Si)/s) for use with pulsed bremsstrahlung sources were tested at DTRA Radiation sources, Linac (Idaho Accelerator Center), Linac (White Sands), hybrid radiation source (NRL), GAMBLE II (NRL), and HERMES III (Sandia). GaAs PCDs for gamma characterization in pulsed reactors (E6 - E7 rad(Si)/s) were calibrated with a Linac (White Sands), checked for high dose rate (E12 rad(Si)/s) response at HERMES III, checked for low dose rate response (5-500 rad(Si)/s) and stability at a Co-60 source (Sandia), and checked for stability, sensitivity, and residual radioactivity at the ACCR reactor (Sandia). Soft X-ray (1 to 15 keV) GaAs PCDs (E2-E6 Watts/cm2) were used to measure the argon plasma free-bound continuum temperature from a plasma radiation source (PRS) and compared with the plasma temperature obtained from line ratio measurements.

Summary form only given. Experiments have been performed at the Z accelerator to study the neutron production from a deuterium gas puff. The current scaling of the neutron production was of primary interest, so shots were fielded at approximately 12 MA, and 16 MA. The shots at both current levels were fielded with similar implosion times. The gas puff nozzle used was a nested shell configuration, with the inner shell extending from 3 to 2 cm, and the outer shell from 3 to 4 cm; the load length was 2 cm. Dopant gases were added to the deuterium (argon and chlorine) to track the implosion characteristics of the gas through X-ray yield and spectroscopy measurements. Indium detectors, as well as lead and beryllium probes were fielded. Neutron time-of-flight measurements were also obtained. Neutron outputs near 1e13 were measured for the 12 MA shot, and greater than 1e13 was observed for the 16 MA shot. These results will be compared with computational predictions and previous neutron measurements from Z-pinch sources

Summary form only given. Large radius implosions of gas-puff Z-pinches are the subject of intense investigation. Such implosions are needed to achieve the high specific energy required to excite K-line radiation from high-atomic-number (e.g. Z>26) radiators, for proper matching with high-current (~10 MA and higher) generators, for continuum radiator concepts that require heating beyond the optimum He/H-like state for K-shell emission, and to utilize more efficiently long-current-rise-time (>100 ns) generators. The key physics issues involve R-T instability mitigation and energy coupling to the radiating plasma by the choice of the initial radial and axial mass profiles. In this talk, recent experimental and theoretical progress in this work are reviewed, including achieving 20-kJ of argon K-shell radiation from a 12-cm-diam. nozzle at 3.5 MA and 200-ns implosion time. The primary experimental testbeds are double-EAGLE (long-pulse mode, 3.5 MA, 210 ns) at TPSD and the Decade Quad (6 MA, 300 ns) at Arnold Engineering Development Center. Supporting experiments on Hawk (0.6 MA, 300 ns) at NRL are also reviewed. Besides the usual soft X-ray and electrical diagnostics, we have developed methods for measuring: the initial gas profile, the L-shell emitting region, the UV and continuum, the initial current flow paths, and the 2-D evolution of the pinch. Recent developments in 2-D radiation-hydrodynamic simulations are also reviewed

Summary form only given. Recent 2-D MHD simulations of large diameter argon gas-puff Z-pinch loads using PLIF (planar laser induced fluorescence) initial density profiles have shown that the radiative emission and absorption characteristics of the plasmas are critically affected by the formation and evolution of nonuniform structures and inhomogeneities. In drive toward the design of large diameter loads having an optimum PRS performance, therefore, it is important to understand the complex nonlinear interaction between these multidimensional structures and the ambient radiation, and the resulting effects on the nonlocal radiative absorption and energy transport processes and the equation of state of the plasma-radiation ensemble. In this study, we will investigate their interaction and effects through a detailed postprocess analysis of the plasmas during the various stages of the implosion process using the AXSTRAN 2D non-LTE radiation ionization dynamics code in conjunction with the SPECAM 3D non-LTE spectra and image synthesizer code. In particular, our analysis will focus on the temporal and spatial evolution of the electron temperature and ion density, and the K- and L-shell radiative power densities. Identification and detailed radiative characterization of the plasma structures are accomplished via a detailed radiative emission and ionization state analysis

Summary form only given. Nozzles for high current, short implosion time (

Summary form only given. Because the energy coupling and the X-ray output of Z-pinch plasma radiation sources are determined by the implosion history, measurements from the initial gas phase, through the MHD implosion phase, to the final pinch phase are needed. Many diagnostics have been developed for the final pinch phase. We have developed a planar laser induced fluorescence (PLIF) technique to characterize the gas puff in the initial phase and demonstrated a laser shearing interferometer (LSI) approach for the implosion and pinch phases on a high current accelerator. These laser based instruments have the advantages of being user-friendly and giving the data quickly. Using the PLIF method, the 2-D gas density and flow velocity profiles of the loads were obtained with sub-mm spatial resolutions for the conditions used in the Z-pinch experiments. From the LSI, the shape of the imploding plasma was determined and the wavelengths of the Rayleigh-Taylor instability were measured. We have also found that the pinch plasma sizes are about twice that measured from the K-shell X-ray pinhole images. The combination of the PLIF and (LSI) measurements enable us to better understand the implosion dynamics and to provide important information needed for simulation codes

Summary form only given. A number of diagnostics have been developed to measure the argon K-shell (~3 keV) X-ray emitting volume and spectrum. However, only ~20% of the load mass participates in the K-shell emission and less than 20% of the total emission falls in that energy band. We have made measurements to determine both the radial emission profile and the emitted spectrum in the XUV (0.1

Summary form only given. In order to implode enough mass to the high specific energies necessary to produce K-shell emission from high Z elements like krypton, large-diameter Z-pinch loads will be required for short current rise time machines, like Z and ZR. For long pulse rise time machines, such as Decade Quad, large diameters are needed for the same reason and, in addition, they are needed to effectively couple the electrical energy that is delivered over a long current rise time to the load. The amount of K-shell emission produced from a large-diameter load has experimentally been shown to depend critically on the initial density distribution. In the work presented here, we investigate the initial gas-puff density distribution's effect on the ability of the plasma to radiate in the K-shell. This study is performed using a modified version of the Air Force's MACH2 magnetohydrodynamic code. The principal modification is the self-consistent addition of a state-of-the-art, computationally efficient, and reasonably accurate equation of state (EOS) and radiation transport model to MACH2. This EOS/radiation model is designed for modeling K-shell emitting plasmas and it is called the tabular collisional radiative equilibrium (TCRE) model. In this study comparisons are made between simulations of, and results obtained from, large-diameter load experiments on the Decade Quad and Double-EAGLE pulsed power generators.

Summary form only given. We have developed large diameter nozzles for long-implosion-time argon z-pinch experiments over the past several years. Results on the Double-EAGLE generator in 2002 with a 12 cm double-shell nozzle (outer shell between 5 and 6 cm; inner shell between 2 and 3 cm) indicated that increased K-shell yield might be obtained with the addition of more mass near the axis, which was implemented by use of a central jet that was connected to the inner shell plenum. In our present work, we have modified the gas valve design by including a third plenum for the central jet. This allows the pressure to be set independently to maximize the K-shell yield and for a separate tracer gas to be introduced that can distinguish plasma parameters between gases originating in the central jet and the inner shell. Experiments utilizing this new system will occur in early 2004. In this paper, we discussed the design and detailed results of the experiments.

Summary form only given. The technique of Planar Laser Induced Fluorescence (PLIF) has been applied to characterize the initial gas distributions produced by 12 cm diameter nozzles, as used on recent Decade Quad and Double-EAGLE Ar Z-pinch experiments. This information is required to understand and simulate the implosion dynamics. A 266 nm, /spl sim/5 ns, /spl sim/5 cm line-focused laser beam passes through the Ar gas puff, which is mixed with a few percent acetone by volume. A gated intensified CCD camera views the fluorescence of the excited acetone molecules from the side. The acetone emission has a short, intense pulse, coincident with the exciting laser pulse, and a weak, slowly decaying phosphorescence. The gas density profiles are obtained from the fluorescence images recorded coincident with the laser. Flow velocities of the gas puff are obtained by capturing the images of the phosphorescence at several delay times relative to the laser pulse. The distribution of the clusters is determined by comparing the PLIF signal with 2-D Rayleigh scattering from the gas puff. These measurements are compared with computer simulations to benchmark and refine the 2-D fluid dynamics models.

The Decade half X-ray radiation simulator will combine the outputs of eight synchronized modules to produce a current of up to 13 MA delivered to a short circuit load in /spl sim/300 ns. Decade is located within the Decade Radiation Test Facility (DRTF) at the Arnold Engineering Development Center, Tullahoma, TN. Decade's output will be used for nuclear weapons effects testing; the DRTF will reach initial operational capability (IOC) in 2007. DoD's X-ray radiation simulator R&D program is focused on maximizing 3.1 keV X-ray fluence from Decade's argon z-pinch. Electric current risetime will be approximately a factor of 3 longer than typically used to drive plasma radiation source (PRS) loads. Scaling to longer current risetime is advantageous in terms of reduced driver cost and complexity. The use of longer pulse drivers, however, requires an increase in the initial diameter of the z-pinch gas puff. The unique challenge is to extend the success with 100 ns current risetime simulators into the realm of the 300 ns current risetime of Decade. As the diameter is increased, increased asymmetry and instability can limit the ability of the load to produce K-shell radiation efficiently. These effects were largely un-quantified until technical investigations were conducted under the auspices of the simulator R&D program. This paper discusses progress, activities and issues in developing the large diameter z-pinch for Decade.

Summary form only given, as follows. The design of gas flow nozzles for optimum K-shell X-ray emission remains an imperfect science. We report on a limited set of tests, using the Double Eagle simulator, evaluating two key factors. The first factor was the detailed form of the nozzle contours: simple linear contours versus curved "aerodynamic" contours intended to minimize turbulence. The second factor was the relative radial concentration of mass in the flow. All tests employed double shell nozzles. While the test set was incomplete, the data strongly imply that details of nozzle shape are relatively unimportant. On the other hand, radial mass distribution is very critical. With twice the mass (ug/cm) in the outer shell than the inner shell, argon K-shell yield was only 5 kJ. With nearly equal masses in the two shells, yield increased dramatically to over 17 kJ, matching the optimum output on Double Eagle for 200 ns implosions. Since the simplest models of z-pinches favor putting most of the mass at the largest radius, these results strongly imply that that configuration is subject to severe disruption by instabilities during the implosion. These results confirm earlier observations that filled-in mass distributions are preferred, and support the concept of snowplow stabilization.

Summary form only given, as follows. We have made streaked spectroscopy measurements of K-shell x-ray emission at the SNL/Albuquerque Z facility for both nested Ni wire arrays and Ar double-shell gas puffs. By doping either of the wire arrays or gas puff shells with a different tracer, Cr or Mn in the case of the wire arrays and Cl for the gas puffs, we can determine when the mass from each is radiating in the K-shell. In general, we find that the inner array or puff mass starts emitting K-shell X rays first and stops emitting before the outer mass does. This result runs counter to a 1D picture in which the arrays do not mix and the inner array mass remains hot and dense longer than the outer array mass.

Summary form only given, as follows. An argon double-shell gas puff source was fielded on Decade Quad, which was configured in the PRS mode with the four modules combined into a single pulse power driver. In a series of six shots, four of which were taken at reduced Marx charge (70 kV vs. 85 kV full charge), we demonstrated 29 kJ of K-shell radiation in an 11 ns FWHM radiation pulse at 4.6 MA peak current. Current scaling from a 4.1 MA, 18 kJ test was 13.6. Plasma parameters were measured with an x-ray pinhole camera and a spectrometer, both recorded with CCD cameras. The electron temperature was 1600 eV and the ion density 1.5/spl times/10/sup 19/ cm/sup -3/. The K-shell emitting diameter was 3.1 nm. Four B-dot probes in a load anode ring measured the current; the yield was measured with a set of three tantalum calorimeters. The four current probes agreed to within 3%, the calorimeters to within 2%. Although there is an insufficient database to be precise; the optimal implosion time was approximately 210 ns; the shot described above had an implosion time of 214 ns. This reflects the fact that the nozzle was designed for 200 ns implosions (/spl eta/=2) on Double-EAGLE and thus did not tap the full potential of Decade Quad, which has a 300 ns quarter period (which would produce /spl eta/=0.7 with the present nozzle). In this paper, we will discuss the design and detailed results of the experiment.

Summary form only given. A 1-2-3-4 cm double-shell nozzle was designed and built in 1999 to study long implosion time gas puff Z-pinches. A test program using the same nozzle on all major US accelerators including Double-EAGLE, Saturn, Decade Quad and Z has recently been completed. In this talk, we will present the performance characteristics of this nozzle. Total yield, K-shell yield, power, pulse-width, implosion times will be presented. Pinch characteristics including size and uniformity will be discussed. Pinch ion densities and electron temperatures will be analyzed. Two different techniques to measure the initial gas density profile will be discussed. Optimization experiments to enhance K-shell radiation will be reviewed. Results of a novel spectroscopic technique to trace the source of the radiation will also be illustrated. The yield performance will also be compared to calculations. This comparison is interesting because all test results on Double-EAGLE, Saturn, Decade Quad and Z use the same nozzle with same ratio of inner to outer shell masses, shell geometries, pre-ionization and pinch length. Finally, since the double-shell gas puff allows implosion of two distinct, not mixed, gases with different atomic numbers, results from preliminary experiments with argon and krypton will also be presented.

Summary form only given. The radial distribution of the ion density and electron temperature in a Z-pinch has been inferred by comparing the measured values of the X-ray power and the ratio of optically thick spectral line intensities with calculated ones for a range of assumed radial distributions. This procedure provided evidence for an on-axis dip in the ion density. A complementary procedure is described to analyze spectra obtained on the DM-2 and Double Eagle accelerators at Maxwell Physics International. In this case, the radially resolved intensities of optically thin dopants added to the pinch were measured using a high resolution Johann spectrometer, the line intensities were Abel inverted and the radial distribution of two line ratios [L/sub /spl alpha//(He/sub /spl alpha//+IC) and IC/He/sub /spl alpha//] were obtained from which the localized electron temperature and density were inferred.

Summary form only given. Previous research on the high-power generators DM2, at Maxwell Physics International, and Saturn, at Sandia National Laboratories, has demonstrated that long-implosion (200-300 ns) PRS sources, both gas puff and wire load, can be sufficiently stable to produce well-assembled pinches and high-power radiation pulses of soft X-rays (1-4 keV). This has substantial implications for reducing the cost and risk of future higher current facilities (e.g. Decade Quad). To extend our knowledge and understanding of long-implosion sources, we are conducting a well-diagnosed series of experiments on long-pulse Double-EAGLE (4 MA at 200 ns). Results from Ar gas puffs, with various nozzles and valves, and Al wire arrays will be presented. Where possible, comparison with short-pulse results will be discussed.

Summary form only given, as follows. In a previous research, an azimuthally symmetric UV source was used to preionize the argon gas puffs in the DM2 plasma radiation source (PRS) experiment. It indicated that the preionization helped to improve the PRS K-shell yield and reduce shot to shot variations. It also revealed that the issues of survivability and replaceability must be addressed for such a preionization source to be used in super-power generator environments. Based on the evaluation of the previous preionizer, a robust new preionizer has been fabricated and fielded on Double-EAGLE during the PRS experiment. Design of the new preionizer and its performance on Double-EAGLE will be presented. Comparison with the previous preionizer will also be discussed.

We have created large diameter, long implosion time, PRS loads that produce a stable pinch and a narrow X-ray pulse. Operation scaled successfully with current from 2 MA on DM2 to 6 MA on Saturn. The K-shell yields are comparable to those produced by short-pulse operation at a similar current. This approach, therefore, allows substantial savings to be realized in the pulsed-power driver cost, complexity and risk.

DECADE Module 2 (DM2) implodes argon gas-puffs in 200-300 ns from initial radii of 2.5-5 cm to generate K-line radiation. An important issue for these experiments is the lower-than-expected K-line radiation associated with such large radius implosions. Preionization may improve the implosion quality by improving the symmetry of the initial current flow. A preionizer is described based on photoionization by ultraviolet (UV) illumination from a flashover source. The preionization is diagnosed using a high-sensitivity interferometer. This UV source produces 1-10% ionization of the outer periphery of the argon gas distribution prior to the arrival of the flashboard plasma. DM2 experiments indicate increased, more reproducible K-shell yields when this preionization system is incorporated.

Summary form only given. Efficient production of soft X-rays (1 to 5 keV) has been achieved in many laboratories using Z-pinch plasma radiation sources (PRS) driven by short pulses of mega-ampere currents. Empirical and theoretical scaling laws for 8 MA with a rise time of 300 ns, coupling >400 kJ to kinetic energy in the Z-pinch.